This invention relates generally to non-rotating drill pipe protectors attached to a drill string, and more particularly, to improved low-friction drill pipe protectors by incorporating a soft elastomer liner and low-friction end pads.
The drilling of holes or bores into underground formations and particularly, the drilling of oil and gas wells, is typically accomplished using a drill bit which is attached to the lower end of an elongated drill string. The drill string is constructed from a number of sections of tubular drill pipe which are coupled at their ends to form the xe2x80x9cdrill stringxe2x80x9d. The drill string extends from the drilling surface into a well or xe2x80x9cwellborexe2x80x9d which is formed by the rotating drill bit. As the drill bit penetrates deeper or further into an underground formation, additional sections of drill pipe are added to the drill string.
Casing is generally installed in the wellbore from the drilling surface to various depths. The casing lines the wellbore to prevent the wall of the wellbore from caving in and to prevent seepage of fluids from the surrounding formations from entering the wellbore. The casing also provides a means for recovering the petroleum if the well is found to be productive.
A drill string is relatively flexible, being subject to lateral deflection, especially at the regions between joints or couplings. In particular, the application of weight onto the drill string or resistance from the drill bit can cause axial forces which in turn can cause lateral deflections. These deflections can result in portions of the drill string contacting the casing or wellbore. In addition, the drilling operation may be along a curved or angled path, commonly known as xe2x80x9cdirectional drilling.xe2x80x9d Directional drilling also causes potential contact between portions of the drill string and the casing or well bore.
Contact between the drill string and the casing and well bore creates frictional torque and drag. In fact, a considerable amount of torque can be produced by the effects of frictional forces developed between the rotating drill pipe and the casing or the wall of the well bore. During drilling operations, additional torque is required while rotating the drill string to overcome this resistance. In addition, the drill string is subjected to increased shock and abrasion whenever the drill string comes into contact with the wall of the well bore or, where lined, the casing. Drilling tools and associated drill string devices encounter similar problems.
To alleviate these problems, drill pipe protectors are typically spaced apart along the length of the drill pipe. These drill pipe protectors were originally made from sleeves of rubber or other elastomeric material which were placed over the drill pipe to keep the drill pipe and its connections away from the walls of the casing and/or formation. Rubber or other elastomeric materials were used because of their ability to absorb shock and impart minimal wear.
Previously available drill pipe protectors have an outside diameter (O.D.) greater than that of the drill pipe joints, and were installed or clamped rigidly onto the drill pipe at a point near the joint connections of each length of drill pipe. The O.D. is specifically sized to be larger than the tool joint, but not too large as to restrict returning fluids which could result in xe2x80x9cpistoningxe2x80x9d of the protector in the hole. Such an installation allows the protector only to rub against the inside wall of the casing as the drill pipe rotates. Although wear protection for the casing is the paramount objective when using such drill pipe protectors, they can produce a significant increase in the rotary torque developed during drilling operations. In instances where there may be hundreds of these protectors in the wellbore at any one time, they can generate sufficient accumulative torque or drag to adversely affect drilling operations if the power required to rotate the drill pipe approaches or exceeds the supply power available.
In response to the problems of wear protection and torque build up, improvements have been directed toward producing drill pipe/casing protectors from various low-friction materials in different configurations. However, such an approach again has only been marginally effective, and oil companies still are in need of an effective means to greatly reduce the wear and frictionally-developed torque normally experienced particularly when drilling deeper wells and deviated wells.
U.S. Pat. No. 5,069,297 to Krueger, et al., assigned to the assignee of the present application, and incorporated herein by reference, discloses a drill pipe/casing protector assembly which has successfully addressed the problems of providing wear protection for the casing and reduced torque build up caused by the drill pipe protectors during drilling operations. The protector sleeve in the ""297 patent rotates with the drill pipe during normal operations in which there is an absence of contact between the protector sleeve and the casing, but the protector sleeve stops rotating, or rotates very slowly, while allowing the drill pipe to continue rotating within the sleeve unabated upon frictional contact between the sleeve and the casing. Thrust bearings are rigidly affixed to the drill pipe at opposite ends of the protector sleeve, and these, in combination with the internal configuration of the protector sleeve, produce a fluid bearing effect in the space between the inside of the sleeve and the outside of the drill pipe. The fluid bearing effect is produced by circulating drilling fluid through the space between the sleeve and the drill pipe so that it reduces frictional drag between the rotating drill pipe and the sleeve when the sleeve stops rotating from contact with the casing.
U.S. Pat. No. 5,803,193, to Krueger, et al., assigned to the assignee of the present application, and incorporated herein in its entirety by reference, discloses a drill pipe/casing protector assembly which provides an enhanced fluid bearing effect that reduces frictional drag between the rotating drill string and the protector sleeve during use.
Although modern drill string protector designs have improved the lubrication and protection of both the drill string and the casing, there is still a need for improved sliding lubrication. In addition, there is a need for hydraulic lift to overcome the heavy normal forces and torques encountered by the operating drill string. This problem is especially significant in extended reach drilling. In long holes and as depth increases, the friction of the drill string against the hole wall increases resulting in difficulty in putting weight on the drill bit or a tendency for the weight to surge forward then reduce in a xe2x80x9cstickionxe2x80x9d type process. Thus, a drill pipe protector that both reduces the torque from the drill string and increases the sliding ability of the drill string against the casing is highly desirable.
Another problem to which the present invention is directed is the reduction of friction between the protector sleeve and the thrust bearings or collars positioned on either end of the sleeve. Improvements in economic value through increased product life without loss of structural integrity is also desirable.
The present invention overcomes the aforementioned problems by providing in one embodiment a drill pipe protector assembly that provides hydraulic lift and improved sliding lubrication to a drill string. The creation of hydraulic lift and forced lubrication reduces wear on the protector and on the casing or well wall as well as reducing sliding friction of the drill pipe/protector combination relative to the casing or well wall.
By providing a drill pipe protector assembly having a fluid pathway which directs a portion of the drilling mud moving through the annular space between the drill pipe protector and the drill pipe to the annular space between the protector and the casing or outer well wall, hydraulic lift is created and sliding lubrication is achieved. By providing shaped channels along the longitudinal length of the outer surface of the protector, increased hydraulic lift is developed.
In one embodiment, the present invention is generally directed to a drill pipe protector which defines a tubular sleeve that fits over the drill pipe. The sleeve is attached to a section of drill pipe and resides over the drill pipe. The sleeve is positioned between the outer diameter of the drill pipe and an associated well casing or well hole. The sleeve is adapted to provide hydraulic lift and lubrication relative to the well casing and thus, increase the proclivity of the drill pipe to slide down the hole while also reducing the development of cutting dams.
More specifically, the drill pipe protector assembly comprises a tubular body having an inner surface and an outer surface and extends along a longitudinal axis between a first end and a second end. The tubular body is adapted to be deployable about the outside of a drill string and within the wellbore or casing. A channel is formed on the outer surface of the body and extends substantially along the longitudinal axis from the first end to the second end. The channel directs the flow of drilling fluid between the outer surface and the inside surface of the casing. An opening extends radially from the inner surface to the outer surface of the tubular body. The opening allows the passage of the drilling fluid from the inner surface to the outer surface.
In this embodiment the protector is a generally cylindrical shaped tubular body having a plurality of spaced apart channels along its outer surface. The outer surface includes a plurality of radially outwardly protruding ridges which extend substantially along the longitudinal axis. The ridges are spaced apart sufficient so as to form the described channels therebetween. At least one, and preferably, all of the channels include an opening which allows the drilling fluid to pass from the inner surface to within the channel.
The sleeve includes a plurality of spaced apart radial openings or diffusor ports which directs a portion of the drilling mud moving longitudinally through the annular space between the inside of the sleeve and drill pipe to the annular space between the outside of the sleeve and the casing or outer well wall. The outside surface of the sleeve also includes a plurality of shaped channels which are in communication with these radial openings. The channels direct the flowing mud to lubricate the outer surface of the sleeve and create hydraulic lift relative to the casing wall.
In another embodiment of the present invention, the drill pipe protector assembly is a tubular sleeve having a plurality of longitudinally extending and radially protruding ridges formed on its outer surface. The ridges or ribs are spaced apart to define channels therebetween and at least some of the channels are configured to define a longitudinally extending channel having a double wedge shape. The double wedge shaped channels form passageways for the longitudinal flow of the drilling mud along the outer surface of the sleeve. Each channel or passageway includes a radially oriented internal passageway that interconnects the drilling fluid passing through the annular space between the sleeve and the drill pipe and the annular space between the outside of the sleeve and the casing. Each double wedge shaped channel defines an increasingly narrower and shallower passageway which transitions to a increasingly wider and deeper passageway along its longitudinal length. The double wedge shape accelerates and then decelerates the flow to create a hydraulic lift relative to the casing wall and also enhance the flow of the drilling mud therebetween.
In another aspect of the present invention, the protector assembly includes a tubular sleeve for use with drill tool assemblies. The sleeve includes channels formed on the outer surface for directing the flow of mud in the annular space between the channels and the casing. In addition, the sleeve includes a plurality of spaced apart radially oriented internal passageways that interconnects the drilling mud passing through the annular space between the sleeve and the drill pipe and the annular space between the outside of the sleeve and the casing.
In another embodiment of the present invention, the protector incorporates low-friction material pads on the external surfaces. The pads are made of Teflon composites. The protector can have a plurality of curved surfaces.
In another embodiment of the present invention, the protector incorporates a multi-stave multi-material sleeve that includes use of a soft elastomeric liner having a preferred hardness of 60 Shore A, although can be in the range of 40-85 Shore A, in a urethane sleeve having a preferred hardness of 95 Shore A, although can be in the range of 75-95 Shore A for urethane, and 75 to 123 Rockwell R for harder plastics. The flexible inner liner material produces a more efficient fluid bearing and thus a lower coefficient of rotational friction between the drill pipe and the sleeve.
Studies have been undertaken to improve the performance of the fluid bearing of a drill pipe protector while providing the same or better strength of previous polyurethane formulations and improving protector assembly economic life. Testing determined that friction losses were manifest between the drill pipe and the protector sleeve on the inside diameter of the sleeve and at the interface between the sleeve and the collar on the ends of the sleeves and collars. The combination of these two sources of friction is the net resultant coefficient of frictional loss per drill pipe protector assembly. Quantification of the rotational frictional loss on the sleeve I.D. and the rotational loss at the interface of the sleeve to the collar varies for different types of materials used for the protector sleeves.
For urethane sleeves with 95 A Shore hardness, approximately 50 to 60% of the total frictional loss comes from the friction between the ends of the sleeve and the collar. The frictional loss between the sleeve I.D. and the drill pipe provides the other significant friction dissipation. The friction between the ends of the sleeve and the collar is the source for the wearing of the ends of the sleeves and, hence, most frequently becomes the factor that limits the useful economic life of the protector sleeves and collars. Therefore, in another embodiment of the present invention, the protector consists of a unique composite sleeve design to reduce frictional forces and wear on the ends of the sleeves and collars without loss of structural integrity. This is accomplished by incorporating low-friction abrasion-resistant end pads integrally molded into the sleeve during the manufacturing process. The end pads are pre-stamped into a preferred configuration wherein the pre-formed low-friction end pad is placed at the bottom of the mold during the manufacturing process. Depending upon the configuration, a metal cage would then be inserted before the urethane is poured into the mold. Low-friction end pads can be positioned at one or both ends of the protector sleeve during the manufacturing process. Alternatively, multiple segments of low-friction abrasion resistant end pads can be positioned at the end of the sleeve, which are placed at the bottom of the mold before the urethane is poured.
These and other features and advantages of the invention will be apparent and more fully understood by those of skill in the art by referring to the following detailed description of the preferred embodiments which is made in reference to the accompanying drawings, a brief description of which is provided below.